Fast optical link control adaptation using a channel monitor

ABSTRACT

An amplifier receives an optical signal including a number of labeled channels via a fiber. The amplifier determines a count of the labeled channels and a spectral distribution of the labeled channels. The amplifier adjusts a parameter of the amplifier based on the count of the labeled channels and the spectral distribution of the labeled channels. The amplifier amplifies the optical signal at an adjusted output gain resulting from adjusting the parameter of the amplifier.

This application is a continuation of U.S. patent application Ser. No.15/049,516 filed Feb. 22, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/675,454 filed Nov. 13, 2012, and issued on Mar.29, 2016 as U.S. Pat. No. 9,300,396, the disclosures of each of whichare herein incorporated by reference in their entirety.

TECHNICAL FIELD

This application relates generally to systems, methods and apparatus forfast optical link control adaptation using a channel monitor and moreparticularly to systems, methods and apparatus for fast optical linkcontrol adaptation using a channel monitor employing a channel labelingsystem.

BACKGROUND

Optical communication systems transmit and receive channels over opticalfiber. When transmitting channels from node to node, if the distancebetween nodes is significant, the channels may need to be amplified.Amplifiers placed in between nodes provide amplification of channels.The amplifiers may be placed between the source node and the destinationnode at certain intervals (e.g., 80 kilometers).

In optical communication systems, reconfigurable optical add-dropmultiplexers (ROADMs) may be used to add and drop channels along theway. For example, when a particular channel reaches its intendeddestination, a ROADM may drop the channel from the system.

When a problem occurs in optical communication systems, channels may belost. Other channel transmission may be affected by the lost channels inthe optical communication systems.

SUMMARY

In accordance with an embodiment, an amplifier receives an opticalsignal including a number of labeled channels. The optical signal iscarried on a fiber. The amplifier determines a count of the labeledchannels and a spectral distribution of the labeled channels. Aparameter of the amplifier is adjusted based on the count of the labeledchannels and the spectral distribution of the labeled channels. Theoptical signal is amplified at an adjusted output gain resulting fromadjusting the parameter of the amplifier.

In an embodiment, a system includes an amplifier. The amplifier includesa channel monitor that receives optical signal including a number oflabeled channels. The channel monitor determines a count of the labeledchannels and a spectral distribution of the labeled channels. Theamplifier includes a pump laser source to amplify the optical signal.The amplifier also includes an amplifier controller to adjust aparameter of the pump laser source based on the count of the labeledchannels and the spectral distribution of the labeled channels tocontrol amplification of the optical signal at an adjusted output gain.

In an embodiment, an amplifier includes a processor and a memorycommunicatively coupled to the processor. The memory to stores computerprogram instructions. When the computer program instructions areexecuted on the processor, the computer program instructions cause theprocessor to perform operations comprising: receiving, at an amplifier,an optical signal including a number of labeled channels, the opticalsignal carried on a fiber; determining a count of the labeled channelsand a spectral distribution of the labeled channels; adjusting aparameter of the amplifier based on the count of the labeled channelsand the spectral distribution of the labeled channels; and amplifyingthe optical signal at an adjusted output gain resulting from adjustingthe parameter of the amplifier.

In an embodiment, a computer readable medium storing computer programinstructions for providing optical link control adaptation, which, whenexecuted on a processor, cause the processor to perform the followingoperations: receiving, at an amplifier, an optical signal including anumber of labeled channels, the optical signal carried on a fiber;determining a count of the labeled channels and a spectral distributionof the labeled channels; adjusting a parameter of the amplifier based onthe count of the labeled channels and the spectral distribution of thelabeled channels; and amplifying the optical signal at an adjustedoutput gain resulting from adjusting the parameter of the amplifier.

These and other advantages of the present disclosure will be apparent tothose of ordinary skill in the art by reference to the followingDetailed Description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a communication network, in accordance with an embodimentof the present application;

FIG. 2 depicts a ROADM communication system, in accordance with anembodiment of the present application;

FIG. 3 depicts details regarding an exemplary transmitter, in accordancewith an embodiment of the present application;

FIG. 4 depicts details regarding an exemplary amplifier, in accordancewith an embodiment of the present application;

FIG. 5 is a flowchart of adjusting power in an optical system, inaccordance with an embodiment of the present application; and

FIG. 6 shows components of a computer that may be used to implement theapplication.

DETAILED DESCRIPTION

FIG. 1 depicts a communication network, in accordance with an embodimentof the present application. FIG. 1 includes a section of a meshcommunication network 100, comprising multiple nodes. A first node 104is located in New York; a second node 105 is located in Philadelphia; athird node 106 is located in Pittsburgh, a fourth node 107 is located inChicago and a fifth node 108 is located in Washington, D.C. Each of thenodes can communicate with any other node by sending signals through anoptical fiber 111, an optical fiber 112, and optical fiber 113, and/oran optical fiber 114 interconnecting the nodes. Each optical fiber maysimultaneously carry many independent signals, including signals fromdifferent sources and/or signals intended for different destinations, byassigning each independent signal a unique wavelength channel. Such ascheme is called wavelength-division multiplexing (WDM).

Suppose now that an operator, system, etc. wishes to transmit data fromfirst node 104, located in New York, to fourth node 107, located inChicago. The data may be transmitted from first node 104 to fourth node107 in the following manner. First node 104 may transmit the data over achannel of an optical fiber to second node 105, located in Philadelphia.Second node 105 may then transmit the channel containing the data tothird node 106, located in Pittsburgh. Third node 106 may then transmitthe channel containing the data to fourth node 107, located in Chicago,which is the destination node. At the same time, data may be transmittedfrom the fifth node 108, located in Washington, to the fourth node 107,located in Chicago, passing through the same intermediary nodes and thesame fibers as the New York—Chicago data, by utilizing a differentwavelength channel. In another embodiment, first node 104 may transmitthe data to fourth node 107 in a different way than the one describedabove.

In an embodiment, data is transmitted on one or more channels. A channelis an optical signal transmitted at a particular wavelength. The datamay be carried on a fiber as a multiplexed optical signal, wherewavelength-division multiplexing (WDM) is used to multiplex multiplechannels onto the multiplexed optical signal.

FIG. 2 depicts a reconfigurable optical add-drop multiplexer (ROADM)communication system, in accordance with an embodiment of the presentapplication. A ROADM communication system 202 includes a ROADM 204located in New York, a ROADM 205 located in Philadelphia, a ROADM 206located in Pittsburgh and a ROADM 207 located in Chicago. If a channeloriginating in New York at ROADM 204 is to be transmitted to ROADM 207at Chicago, the channel may then be transmitted to ROADM 207 via one ormore intermediary ROADMs. For example, the intermediary ROADMs may beROADM 205 located in Philadelphia and ROADM 206 located in Pittsburgh.

Each ROADM can add and/or drop optical signals and/or channels carriedon a multiplexed optical signal. Data transmitted between the ROADMs maybe carried on fiber. Data transmitted between ROADM 204 and ROADM 205 iscarried on fiber 232. Data transmitted between ROADM 205 and ROADM 206is carried on fiber 234. Data transmitted between ROADM 206 and ROADM207 is carried on fiber 236. In an embodiment, multiple fibers may beused to carry the data. In an embodiment, a multiplexed optical signalincluding multiple channels may be carried on fiber usingwavelength-division multiplexing (WDM).

In order to transmit multiplexed optical signals between each pair ofsequential ROADMs (ROADM 204, ROADM 205, ROADM 206, and ROADM 207), themultiplexed optical signals may require amplification, as the distancebetween each pair of ROADMs is significantly large (e.g., greater than80 kilometers). The amplification may be provided by one or moreamplifiers, represented in FIG. 2 as triangles. The amplifiers may beplaced at certain distances from each other and the ROADMs. For example,each amplifier may be located within 80 kilometers of each other or ofanother ROADM. Therefore, the channel may be amplified every 80kilometers. In an embodiment, the amplifiers may be inline amplifiers.

FIG. 2 depicts amplifier 210, amplifier 211 and amplifier 212 which arelocated between ROADM 205, located in Philadelphia, and ROADM 206,located in Pittsburgh. In an exemplary embodiment, the distance betweenamplifiers 210 and 211, the distance between amplifier 211 and 212, thedistance between ROADM 205 and amplifier 210 and the distance betweenamplifier 212 and ROADM 206 may be equivalent to 80 kilometers.

In an embodiment, each ROADM may be connected to one or moretransmitters and receivers. At a ROADM, a channel may be added ordropped from the multiplexed optical signal. When a new channel is to beadded at a source ROADM, the channel from a transmitter may bemultiplexed onto the multiplexed optical signal at the source ROADM.When the channel reaches a destination ROADM, the channel isdemultiplexed (e.g., dropped) at the destination ROADM (e.g., to thereceiver). The demultiplexed channel is then used to retrieve theinformation transmitted on that channel.

ROADM 205 is connected to a transmitter 216 and a receiver 217. ROADM206 is connected to a transmitter 222 and a receiver 223. The ROADMsdepicted in FIG. 2 may correspond to the nodes depicted in FIG. 1. Forexample, ROADM 204, connected to a transmitter 214 and a receiver 215may correspond to first node 104, in FIG. 1. Similarly, ROADM 207,connected to a receiver 218 and a transmitter 219, may correspond tofourth node 107, in FIG. 1. In the embodiment depicted by FIG. 2, eachROADM is connected to at least one transmitter and at least onereceiver. In an embodiment, a transmitter and a receiver may be internalto a ROADM or a ROADM may have no direct connections to receivers ortransmitters.

Although FIG. 2 depicts ROADMs, fixed optical add-drop multiplexers(OADMs) may also be used.

Suppose that first data is to be transmitted on a first channel from NewYork to Chicago and second data is to be transmitted on a second channelfrom Philadelphia to Chicago. The first channel including the first datais added to the multiplexed optical signal on fiber 232 by transmitter214 at ROADM 204 to be received from fiber 236 by receiver 218 at ROADM207. The second channel including the second data is multiplexed ontothe multiplexed optical signal on fiber 234 by transmitter 216 at ROADM205 received on fiber 236 by receiver 218 at ROADM 205. Suppose now thata problem occurs in ROADM communication system 202. The problem mayinclude one or more of the amplifiers failing, a fiber cut, atransmitter failure, etc. Some of the channels may continue to betransmitted across the communication system, while other channels may beaffected by the problem. For example, if a fiber cut occurs betweenROADM 204 and ROADM 205, a failure in the transmission (and reception)of the first channel will occur. The first channel may be lost, causinga sudden reduction by a factor of two (i.e., −3 dB) in the total opticalpower entering the first amplifier between Philadelphia and Chicago,amplifier 210. Amplifier 210 may respond to the sudden drop in totalinput power by increasing gain, triggering a sudden increase in theoptical power output in the surviving optical channel wavelength. Theresulting power transient may propagate down the chain of amplifiers toChicago, ultimately overloading the receiver and causing errors oroutages in the recovered data stream. Since a WDM system may carry asmany as 96 wavelength channels, a fiber cut can easily reduce the inputpower to an amplifier by more than 10 dB, causing very severe powertransients in the surviving channels. In a case when there are multiplesurviving channels, the magnitude of the amplifier gain transient mayvary with wavelength, causing an imbalance among the formerly balancedchannel powers. This power imbalance depends not only on the number ofchannels lost but also on each of the channel's position in the spectrum(i.e., the imbalance may shift depending on which specific wavelengthswere lost and which specific wavelength channels are surviving).Therefore, the channel imbalance cannot be corrected by only measuringthe surviving power or by only measuring the number of channels lost.

One solution to the above problem is to inject “reservoir” channels atthe first ROADM following a fiber cut to compensate for the missingpower and location of the lost channels. However, this approach may beexpensive and complicated, involving extra light sources and fastattenuator hardware. Setting channels aside for reservoir service alsoreduces the number of data channels carried by the system. Therefore,injecting of reservoir channels may be increase cost and reduce datathroughput.

According to an advantageous embodiment, amplifiers perform an outputpower adjustment based on the number of channels present as well astheir location in the optical spectrum. When a problem occurs (e.g.,during a fiber cut), some channels are lost and the amplifier can beadjusted very quickly for the new number of channels and their locationin the optical spectrum. Embodiments of the present disclosure providean easier and more cost effective solution in which each amplifier canbe controlled using localized control loops to set to the optimumoperating point for that amplifier within a few microseconds. Eachamplifier may make a smarter decision having localized knowledge withoutrequiring extra light sources or setting aside reservoir channels.

Thus, in order to deal with a problem occurring in the ROADMcommunication system, one or more of the amplifiers may need todetermine which channels are surviving and the location of thosechannels in the optical spectrum. The amplifiers may then determine thatadjustment of pump power, gain, and/or tilt is required. Detailsregarding the amplifiers determining which channels remain and thelocation of the channels in the spectrum are described herein.

In various embodiments, any type of amplifiers may be used. For example,Erbium-doped-fiber amplifiers (EDFAs), Raman amplifiers, andsemiconductor optical amplifiers or other types of amplifiers can beused to amplify the channel.

FIG. 3 depicts details regarding an exemplary transmitter, in accordancewith an embodiment of the present application. In the depictedembodiment, details regarding transmitter 216 are shown. However, anytransmitter (e.g., transmitter 214, etc.) may include similar details astransmitter 216. Transmitter 216 includes a light source 303, amodulator 310, and a channel labeling system 302. A data signal that iscarried on fiber 301 may be input into transmitter 216. Alternatively,the input data might arrive on multiple fibers or on one or moreelectrical conductors. The data signal is transmitted to modulator 310of channel transmitter 216. The modulator 310 may be coupled to a lightsource 303. The light source 303 may be a laser, such as a semiconductorlaser. The modulator 310 modulates the data signal onto an opticalcarrier wave emitted from the light source 303 to create a channel.

In order to label the channel at a source (e.g. at transmitter 216),channel labeling system 302 assigns a channel label to the outgoingoptical signal. The label may be unique throughout the network, or thesame label may be reused at another location in the network. However,the label must be arranged such that that the same label is never usedfor two different channels carried in the same fiber. A simple way toguarantee that the same label is not used for two different channelscarried in the same fiber is to use one label per wavelength. Since notwo channels in a single fiber can be allowed to share the samewavelength, no two channels in a single fiber will share the same label.Channel labeling system 302 may assign its label autonomously, or mayreceive label assignments from a label controller outside thetransmitter 216. The labeled optical signal may be carried onto outputfiber 234. In an embodiment, the label may be inserted into the headerof the payload of the channel. In another embodiment, channel labelingsystem 302 encodes and reshuffles the incoming bit stream in a digitalencoding process in order to provide a channel label that can be read byan inexpensive, low speed label receiver capable of reading labels frommultiple channels simultaneously. Additional information regarding achannel labeling system can be found in M. D. Feuer and V. A.Vaishampayan, “Rejection of interlabel crosstalk in a digital lightpathlabeling system with low-cost all-wavelength receivers”, IEEE J.Lightwave Technol., vol. 24, pp. 1121-1128 (2006). A few extra bits maybe added into the channel data stream, representing coding overhead of˜1%. Alternate techniques for creating the channel labels may includeshifting the carrier frequency, amplitude, polarization, or othercharacteristic of the light source 303 before the light reaches the datamodulator 310. In yet another embodiment, the optical signal emergingfrom the data modulator 310 may be overmodulated before beingtransmitted to the output fiber. (See Y. Hamazumi and M. Koga,“Transmission capacity of optical path overhead transfer scheme usingpilot tone for optical path network,” IEEE J. Lightwave Technol., vol.15, pp. 2197-2205 (1997)). When this overmodulation uses a singlefrequency sinusoidal wave, the method is sometimes referred to as “pilottones”. In one embodiment, the channel labeling system 302 may create anauxiliary data transmission channel, in which the label is sent as amessage. In an embodiment, a low speed label receiver may receive themessage simultaneously with label messages on other wavelengths in thefiber, contributing to rapid readout of a count and spectraldistribution of the channels entering an optical amplifier. Additionaldetails regarding the labeling of an optical signal and/or channel aredescribed in U.S. Pat. No. 7,580,632 by Feuer et al., which isincorporated herein by reference in its entirety.

Transmitter 216 may include additional components (not shown).

FIG. 4 depicts details regarding an exemplary amplifier, in accordancewith an embodiment of the present application. Amplifier 212 includes atap coupler 402, a channel monitor 404, an amplification medium 410, anamplifier controller 406, and a pump laser source 408. As a multiplexedoptical signal carried on fiber 234 is received by amplifier 212, theoptical signal is input to splitter 402. Tap coupler 402 may split themultiplexed optical signal unto two output paths in order to input theoptical signal to channel monitor 404 and to amplification medium 410.Channel monitor 404 receives the multiplexed optical signal andmonitors/reads the labels associated with the channels on themultiplexed optical signal. For example, the labels may provide anidentifier associated with each channel, which allows amplifier 212 todetermine details regarding each channel in order to determine thenumber of channels present and identify which channels are present. Inan embodiment, channel monitor 404 may also measure the optical powerpresent in each channel as well as their number and arrangement.Amplifier controller 406 calculates how much the pump power must beadjusted based on channel information (e.g., how many/which channelsremain) from channel monitor 404 and adjusts those parameters of pumplaser source 408. In an embodiment, pump laser source 408 may includeone or multiple pump lasers. If pump laser source 408 includes more thanone pump laser, the amplifier controller 406 may adjust each pump powerfor each pump laser separately. Pump laser source 408 provides energyfor the amplifying medium 410, enabling amplifying medium 410 to amplifythe multiplexed optical signal. Amplifier controller 406 controls pumplaser source 408 by adjusting the parameter (e.g. pump power of eachpump laser) of pump laser source 408 such that the multiplexed opticalsignal is amplified at an output power that is appropriate for thenumber and the spectral distribution of the remaining channels. Theadjusted channel is then carried on a fiber onto the next amplifier,ROADM, destination, etc. In an embodiment, amplifier controller 406 mayalso control a variable optical attenuator (not shown) that may be apart of the amplifier 212 in order to attain the needed output power andgain tilt. In another embodiment, the amplifier controller may alsocontrol a variable gain tilt element (not shown) included as part of theamplifier 212 in order to attain the same goals. When the amplifier 212includes multiple sections of amplifying medium, the amplifiercontroller may control pump power to any or all of the multipleamplifying medium sections.

In an embodiment of the present application, the optical amplifiers areindividually able to determine details regarding incoming channels and,in turn, can adjust power, gain, and/or tilt. In order for amplifier 212in FIG. 4 to perform adjustments (e.g., adjust power) of the channelswhen a problem occurs in the optical communication network, amplifier212 needs to determine the wavelengths associated with each incomingchannels and a number of incoming channels. Amplifier 212 can determinethe wavelengths and a number of channels using channel monitor 404.Channel monitor 404 reads a label assigned to each incoming channel(e.g., assigned by a source transmitting the channel). Therefore,amplifier 212 is provided a clear knowledge of the number of channelsand where they are located in the spectrum in order to setup eachamplifier with only a local control loop that adjusts each amplifier byitself to the optimum settings.

FIG. 5 is a flowchart of adjusting power in an optical system, inaccordance with an embodiment of the present application. One or moreoptical signals having particular wavelengths make up one or morechannels. One or more channels are transmitted from a source (e.g.,transmitter 216) to a destination (e.g., receiver 218). The channelspass through one or more amplifiers, including amplifier 212.

At step 502, an optical signal including a number of labeled channels isreceived at an amplifier. The optical signal is carried on a fiber. Forexample, a multiplexed optical signal including a number of labeledchannels is received at channel monitor 404 of amplifier 212. Themultiplexed optical signal is carried on fiber 234 and each channel islabeled by channel labeling system 302 at a transmitter (e.g., at asource) which added the channels to the multiplexed optical signal. Inan embodiment, the number of labeled channels may include one channel ormultiple channels.

Prior to amplifier 212 receiving the multiplexed optical signal, each ofthe multiple labeled channels is labeled by a channel labeling system.The labels include information regarding each respective channel,including the wavelength of the channel.

At step 504, a count of the labeled channels and a spectral distributionof the labeled channels is determined. Channel monitor 404 in amplifier212 determines a count (e.g., a number) of the labeled channels and aspectral distribution of the labeled channels in the multiplexed opticalsignal. Each labeled channel includes a tag and/or a label that can beread by amplifier 216 (and channel monitor 404) in a low cost fashion.Channel monitor 404 reads the label of the labeled channels in order todetermine a number and a spectral distribution of the labeled channels.The spectral distribution may include a frequency. The spectraldistribution may also include the optical power level of an individualchannel.

When channel monitor 404 receives the multiplexed optical signal,channel monitor 404 may decode a portion of a channel transmitted on themultiplexed optical signal to identify the channel and the channel'slocation in an optical spectrum. If multiple channels are received bychannel monitor 404, channel monitor 404 decodes each label associatedwith each of the labeled channels to determine a respective uniqueidentifier associated with respective wavelengths corresponding to eachof the multiple labeled channels. The unique identifier is coded intothe channel by the source of the channel (e.g., channel labeling system302).

Suppose that a loss of one of the labeled channels is detected.Specifically, channel monitor 404 in amplifier 212 detects a loss of oneof the labeled channels. The loss may result from an amplifier failingalong the transmission, a fiber cut between ROADMs or as a result ofother failures and/or problems. In an embodiment, as a result of aproblem, some labeled channels may disappear and channel monitor 404 isable to detect the disappearance. In an embodiment, the loss of one (ormore) of the labeled channels results in an optical transient. That is,a temporary fast change of state of the channel occurs (e.g.,oscillation results in a sudden rise in power followed by a sudden dropin power) and the loading of amplifiers is affected.

Suppose that the fiber cut occurs between ROADM 204 located in New Yorkand ROADM 205 located in Philadelphia. Prior to the fiber cut, ROADM 205may have been transmitting channels at 80 wavelengths and after thefiber cut, the number is reduced to 30 wavelengths. The remainingchannels experience a temporary fluctuation in gain due to the fibercut. ROADM 205 must continue to transmit the remaining channels (e.g.,at the 30 wavelengths), which are not lost, onto ROADM 206, ROADM 207,etc.

In an embodiment, if the transient continues, other remaining labeledchannels may experience channel loading and the other remaining labeledchannels may lose power. This may lead to an outage of the otherremaining labeled channels. However, the present application performsadjustments in order to cope with the lost channels.

Channel monitor 404 determines a remainder of the labeled channels(e.g., by reading the tag and/or label of the labeled channels). Inorder to deal with the loss of one or more labeled channels, amplifier212 needs to be adjusted very quickly for the new number of labeledchannels and the location of the labeled channels in the spectrum.

As described above, channel monitor 404 determines, for each of thelabeled channels, a location in a spectrum associated with each of theremainder of the labeled channels. Channel monitor 404 determinesexactly how many channels are present and where these channels arelocated in the spectrum by reading the label included in each channel.

As described above, the channel is coded with the label by a source thattransmits the channel. Suppose that the channel originates from NewYork. Transmitter 214 may code the channel with the label. Channelmonitor 404 decodes the data to determine the label and thus, channelmonitor 404 determines the location in the optical spectrum of thechannel(s).

At step 506, a parameter of the amplifier is adjusted based on the countof the labeled channels and the spectral distribution of the labeledchannels. For example, amplifier controller 406 adjusts a parameter ofpump laser source 408 of amplifier 212 based on the count and thespectral distribution of the labeled channels in the multiplexed opticalsignal. For example, if the original load of 80 wavelengths is reducedto a cohort of 30 surviving channels, the amplifying medium 410 does notrequire as much energy in order to amplify the new, lower channel load.So the pump laser source may be directed to reduce its pump powers to˜40% of its pump power under full load. If pump power adjustment doesnot control output power and gain with adequate accuracy, the amplifiercontroller may also direct adjustments of a variable optical attenuatorand/or a gain-tilt element, in combination with, e.g., a reduction ofthe pump power to 70% of its original value.

At step 508, the optical signal is amplified at an adjusted output gainresulting from adjusting the parameter of the amplifier. Amplifiercontroller 406 adjusts the parameter of pump laser source 408. Adjustingthe parameter pump laser source 408 results in amplification of themultiplexed optical signal at an adjusted output gain. Thus, amplifier212 can locally make fast adjustments to the power for amplifying theoptical signal based on the current number and the current spectraldistribution of channels in the optical signal at the amplifier, whichmay be beneficial over a centralized control loop.

The amplified optical signal (at the adjusted output gain) is thentransmitted from amplifier 212, on fiber 234 to a next amplifier, ROADM,receiver, destination, etc.

In the present application, it is desirable to have each amplifier reactoptimally to the lost channels. Localized amplifiers may not have theknowledge of the number and location of each channel. In the presentapplication, the amplifier is provided a way to very quickly and cheaplysense how many channels are present and each channels location in theoptical spectrum. Additionally, an amplifier may detect total power ofthe amplifier to adjust the pump laser source inside the amplifierquickly, reacting optimally to the transient.

In an embodiment, instead of using expensive and complex additionalhardware, the present application gives each local amplifier a clearknowledge of the amount of channels and where they are located in thespectrum to setup each amplifier with only a local control loop thatadjusts each amplifier by itself to the optimum settings.

In various embodiments, the method steps described herein, including themethod steps described in FIG. 5, may be performed in an order differentfrom the particular order described or shown. In other embodiments,other steps may be provided, or steps may be eliminated, from thedescribed methods.

Systems, apparatus, and methods described herein may be implementedusing digital circuitry, or using one or more computers using well-knowncomputer processors, memory units, storage devices, computer software,and other components. Typically, a computer includes a processor forexecuting instructions and one or more memories for storing instructionsand data. A computer may also include, or be coupled to, one or moremass storage devices, such as one or more magnetic disks, internal harddisks and removable disks, magneto-optical disks, optical disks, etc.

Systems, apparatus, and methods described herein may be implementedusing computers operating in a client-server relationship. Typically, insuch a system, the client computers are located remotely from the servercomputer and interact via a network. The client-server relationship maybe defined and controlled by computer programs running on the respectiveclient and server computers.

Systems, apparatus, and methods described herein may be used within anetwork-based cloud computing system. In such a network-based cloudcomputing system, a server or another processor that is connected to anetwork communicates with one or more client computers via a network. Aclient computer may communicate with the server via a network browserapplication residing and operating on the client computer, for example.A client computer may store data on the server and access the data viathe network. A client computer may transmit requests for data, orrequests for online services, to the server via the network. The servermay perform requested services and provide data to the clientcomputer(s). The server may also transmit data adapted to cause a clientcomputer to perform a specified function, e.g., to perform acalculation, to display specified data on a screen, etc. For example,the server may transmit a request adapted to cause a client computer toperform one or more of the method steps described herein, including oneor more of the steps of FIG. 5. Certain steps of the methods describedherein, including one or more of the steps of FIG. 5, may be performedby a server or by another processor in a network-based cloud-computingsystem. Certain steps of the methods described herein, including one ormore of the steps of FIG. 5, may be performed by a client computer in anetwork-based cloud computing system. The steps of the methods describedherein, including one or more of the steps of FIG. 5, may be performedby a server and/or by a client computer in a network-based cloudcomputing system, in any combination.

Systems, apparatus, and methods described herein may be implementedusing a computer program product tangibly embodied in an informationcarrier, e.g., in a non-transitory machine-readable storage device, forexecution by a programmable processor; and the method steps describedherein, including one or more of the steps of FIG. 5, may be implementedusing one or more computer programs that are executable by such aprocessor. A computer program is a set of computer program instructionsthat can be used, directly or indirectly, in a computer to perform acertain activity or bring about a certain result. A computer program canbe written in any form of programming language, including compiled orinterpreted languages, and it can be deployed in any form, including asa stand-alone program or as a module, component, subroutine, or otherunit suitable for use in a computing environment.

A high-level block diagram of an exemplary computer that may be used toimplement systems, apparatus and methods described herein is illustratedin FIG. 6. Computer 600 includes a processor 601 operatively coupled toa data storage device 602 and a memory 603. Processor 601 controls theoverall operation of computer 600 by executing computer programinstructions that define such operations. The computer programinstructions may be stored in data storage device 602, or other computerreadable medium, and loaded into memory 603 when execution of thecomputer program instructions is desired. Thus, the method steps of FIG.5 can be defined by the computer program instructions stored in memory603 and/or data storage device 602 and controlled by the processor 601executing the computer program instructions. For example, the computerprogram instructions can be implemented as computer executable codeprogrammed by one skilled in the art to perform an algorithm defined bythe method steps of FIG. 5. Accordingly, by executing the computerprogram instructions, the processor 601 executes an algorithm defined bythe method steps of FIG. 5. Computer 600 also includes one or morenetwork interfaces 604 for communicating with other devices via anetwork. Computer 600 also includes one or more input/output devices 605that enable user interaction with computer 600 (e.g., display, keyboard,mouse, speakers, buttons, etc.).

Processor 601 may include both general and special purposemicroprocessors, and may be the sole processor or one of multipleprocessors of computer 600. Processor 601 may include one or morecentral processing units (CPUs), for example. Processor 601, datastorage device 602, and/or memory 603 may include, be supplemented by,or incorporated in, one or more application-specific integrated circuits(ASICs) and/or one or more field programmable gate lists (FPGAs).

Data storage device 602 and memory 603 each include a tangiblenon-transitory computer readable storage medium. Data storage device602, and memory 603, may each include high-speed random access memory,such as dynamic random access memory (DRAM), static random access memory(SRAM), double data rate synchronous dynamic random access memory (DDRRAM), or other random access solid state memory devices, and may includenon-volatile memory, such as one or more magnetic disk storage devicessuch as internal hard disks and removable disks, magneto-optical diskstorage devices, optical disk storage devices, flash memory devices,semiconductor memory devices, such as erasable programmable read-onlymemory (EPROM), electrically erasable programmable read-only memory(EEPROM), compact disc read-only memory (CD-ROM), digital versatile discread-only memory (DVD-ROM) disks, or other non-volatile solid statestorage devices.

Input/output devices 605 may include peripherals, such as a printer,scanner, display screen, etc. For example, input/output devices 605 mayinclude a display device such as an organic light-emitting diode (OLED)display, an electrophoretic ink (E Ink) display, a cathode ray tube(CRT) or liquid crystal display (LCD) monitor for displaying informationto the user, a keyboard, and a pointing device such as a mouse or atrackball by which the user can provide input to computer 600.

Any or all of the systems and apparatus discussed herein, includingfirst node 104, second node 105, third node 106, fourth node 107, fifthnode 108, ROADM 204, ROADM 205, ROADM 206, ROADM 207, transmitter 214,receiver 215, transmitter 216, receiver 217, receiver 218, transmitter219, transmitter 222, receiver 223, amplifier 210, amplifier 211,amplifier 212, channel labeling system 302, modulator 310, light source303, tap coupler 402, channel monitor 404, pump laser source 408,amplifying medium 410 and amplifier controller 406, may be implementedusing a computer such as computer 600.

One skilled in the art will recognize that an implementation of anactual computer or computer system may have other structures and maycontain other components as well, and that FIG. 8 is a high levelrepresentation of some of the components of such a computer forillustrative purposes.

The foregoing Detailed Description is to be understood as being in everyrespect illustrative and exemplary, but not restrictive, and the scopeof the disclosure disclosed herein is not to be determined from theDetailed Description, but rather from the claims as interpretedaccording to the full breadth permitted by the patent laws. It is to beunderstood that the embodiments shown and described herein are onlyillustrative of the principles of the present application and thatvarious modifications may be implemented by those skilled in the artwithout departing from the scope and spirit of the application. Thoseskilled in the art could implement various other feature combinationswithout departing from the scope and spirit of the application.

The invention claimed is:
 1. A method comprising: receiving, at anamplifier, an optical signal; detecting a plurality of labeled channelsof the optical signal, wherein a number of the plurality of labeledchannels being received is less than a number of labeled channelspreviously received; decoding each label of the plurality of labeledchannels to determine a respective wavelength corresponding to each ofthe plurality of labeled channels; determining a spectral distributionof the plurality of labeled channels based on the decoding; adjusting aparameter of the amplifier based on the number of labeled channels beingreceived and the spectral distribution of the plurality of labeledchannels; and amplifying the optical signal received based on theadjusting.
 2. The method of claim 1, wherein the adjusting a parameterof the amplifier comprises adjusting a variable attenuator of theamplifier.
 3. The method of claim 2, wherein the adjusting a parameterof the amplifier further comprises adjusting a variable tilt element ofthe amplifier.
 4. The method of claim 1, wherein the adjusting aparameter of the amplifier comprises adjusting a pump laser source ofthe amplifier.
 5. The method of claim 1, further comprising: measuringan optical power of each of the plurality of labeled channels, whereinthe adjusting a parameter of the amplifier is further based on theoptical power of each of the plurality of labeled channels.
 6. Themethod of claim 5, wherein the adjusting a parameter of the amplifier isfurther based on a power imbalance among each of the plurality oflabeled channels.
 7. The method of claim 1, wherein the number oflabeled channels being received is less than the number of labeledchannels previously received due to a problem with a fiber used totransmit the optical signal to the amplifier.
 8. An apparatuscomprising: a processor; and a memory to store computer programinstructions, the computer program instructions when executed by theprocessor cause the processor to perform operations comprising:receiving an optical signal; detecting a plurality of labeled channelsof the optical signal, wherein a number of the plurality of labeledchannels being received is less than a number of labeled channelspreviously received; decoding each label of the plurality of labeledchannels to determine a respective wavelength corresponding to each ofthe plurality of labeled channels; determining a spectral distributionof the plurality of labeled channels based on the decoding; adjusting aparameter based on the number of labeled channels being received and thespectral distribution of the plurality of labeled channels; andamplifying the optical signal received based on the adjusting.
 9. Theapparatus of claim 8, wherein the adjusting a parameter comprisesadjusting a variable attenuator.
 10. The apparatus of claim 9, whereinthe adjusting a parameter further comprises adjusting a variable tiltelement.
 11. The apparatus of claim 8, wherein the adjusting a parametercomprises adjusting a pump laser source.
 12. The apparatus of claim 8,the operations further comprising: measuring an optical power of each ofthe plurality of labeled channels, wherein the adjusting a parameter isfurther based on the optical power of each of the plurality of labeledchannels.
 13. The apparatus of claim 12, wherein the adjusting aparameter is further based on a power imbalance among each of theplurality of labeled channels.
 14. The apparatus of claim 8, wherein thenumber of labeled channels being received is less than the number oflabeled channels previously received due to a problem with a fiber usedto transmit the optical signal.
 15. A computer readable storage devicestoring computer program instructions, which, when executed by aprocessor, cause the processor to perform operations comprising:receiving an optical signal; detecting a plurality of labeled channelsof the optical signal, wherein a number of the plurality of labeledchannels being received is less than a number of labeled channelspreviously received; decoding each label of the plurality of labeledchannels to determine a respective wavelength corresponding to each ofthe plurality of labeled channels; determining a spectral distributionof the plurality of labeled channels based on the decoding; adjusting aparameter based on the number of labeled channels being received and thespectral distribution of the plurality of labeled channels; andamplifying the optical signal received based on the adjusting.
 16. Thecomputer readable storage device of claim 15, wherein the adjusting aparameter comprises adjusting a variable attenuator.
 17. The computerreadable storage device of claim 16, wherein the adjusting a parameterfurther comprises adjusting a variable tilt element.
 18. The computerreadable storage device of claim 16, wherein the adjusting a parametercomprises adjusting a pump laser source.
 19. The computer readablestorage device of claim 16, the operations further comprising: measuringan optical power of each of the plurality of labeled channels, whereinthe adjusting a parameter is further based on the optical power of eachof the plurality of labeled channels.
 20. The computer readable storagedevice of claim 19, wherein the adjusting a parameter is further basedon a power imbalance among each of the plurality of labeled channels.